Four granite provinces have been delineated each with its own distinctive pattern of mineralization. 1. The Main Range Province. Endogenous greisen-bordered vein swarms of cassiterite and wolframite. 2. The Eastern Province. Magnetite–cassiterite skarns ± base metal sulphides with antimony in Thailand. 3. The Western (Peninsular Thailand–Burma) Province. Endogenous greisen-bordered vein swarms and pegmatites of cassiterite and wolframite. 4. The North Thailand Migmatitic Province. Endogenous vein and skarn replacement scheelite and fluorite deposits with some tin and local antimony. In all provinces, but particularly in the Main Range, granitoids designated as two-phase variants have been recognized where xenocrysts and xenoliths of coarse, primary texture granite are enclosed in, and corroded by an invasive, equigranular quartzo–feldspathic matrix. These rocks form an essential part of the granite sequence in all provinces and have probably resulted from the infiltration and disruption of the host granite by late stage magmatic fluids. Whole rock geochemistry from Peninsular Malaysia shows that the granites from the Main Range and Eastern Provinces comprise two contrasted suites which correspond approximately to the I and S-type categories advocated by Chappell & White (1974). In addition it is shown that individual plutons within batholiths in the two provinces have distinctive geochemical parameters. Variation diagrams of plutons having the intrusive sequence primary texture granite—two-phase granite—microgranite show linear trends with increasing SiO 2 , Na 2 O, Rb, W, Sn and U, and decreasing Sr, Ba, Th and all other major elements.

New K/Ar mineral ages from the Barisan Mountains of southern Sumatra suggest four main periods of plutonic activity: Miocene-Pliocene (20–5 Ma), Early Eocene (60–50 Ma), Mid-Late Cretaceous (117–80 Ma) and Jurassic-Early Cretaceous (203–130 Ma). These and all other published ages from exposed plutons in western Sumatra indicate a further period of plutonic activity in the Permian (287–256 Ma). They also suggest either that Early Mesozoic activity began in the Late Triassic, or that there were two distinct magmatic cycles, one in the Late Triassic to Early Jurassic (220–190 Ma) and one extending from the Mid-Jurassic to Early Cretaceous (170–130 Ma). In addition, poorly controlled ages from eastern Sumatra indicate that the important Triassic to Early Jurassic (240–195 Ma) tin-belt magmatism of the peninsular Malaysia Main Range Province extends into that area. Preliminary geochemical studies on the Mesozoic granitoids of the Barisan Range of southern Sumatra confirm that they are calc-alkaline, I-type, metaluminous, subduction-related volcanic arc granites (VAG). They broadly correspond to the southerly extension of a combination of the Central Valley and Western Granite Provinces of Thailand and Burma, and underline the fact that there has been a history of subduction-related magmatism along the southwestern edge of Sundaland since earliest Mesozoic times. The plutonic suites are crudely arranged in subparallel, locally overlapping, NW-SE trending belts, focused along deep-seated faults that have acted as magmatic conduits. It is proposed as a preliminary model that breaks in plutonic activity broadly correspond to changes in approach angle and/or rate of subduction, and that in some instances at least they relate to periods of collision and accretion of allochthonous material (terranes, slivers or blocks) of both oceanic and continental character. At least two such events seem to have occurred during the Mesozoic-Cenozoic tectono-plutonic evolution of Sumatra. One in the early Middle Cretaceous reflects collision and accretion of the oceanic Woyla terranes, and one in the latest Cretaceous is possibly related to collision of a continental sliver/block, the West Sumatra terrane, to the Sundaland margin.

A sector of the Peruvian Coastal Batholith 120 km long has been mapped in detail. Little altered volcanics of Cretaceous and Lower Tertiary age make up the bulk of the country rocks and these and their structures are flagrandy cross-cut by a great composite intrusion in which some 16 distinct petrographic units are distributed in many time separated plutons. Though tonalites bulk large, substantial volumes of basic and acid rocks are involved in a clearly marked basic to acid sequence, a primary rhytiim, in the distribution of which there is often a marked symmetry: gabbros on the flanks, tonalites and quartz diorites internally and in a medial position there are centred complexes in which adamellites are particularly important. Each of the main petrographic units involved a secondary rhythm of in situ, high level, differentiation in their emplacement. The adamellites have followed earlier arcuate basic intrusions and the resulting associations of multiple plutons and ring dykes are thought to represent the basal wrecks of volcanoes which were active over the entire intrusion history of the batholith. The space problem has not been fully solved and the resolution of this problem will depend on structural analysis of the envelope over a wide area. It has however been demonstrated that stoping and cauldron subsidence were important and because the attitude of many of the main contacts was controlled by contemporaneous fracturing it seems that a general uplift on faults may have provided some of the space for intrusion.

The Andean geosyncline in Peru is divided into faulted strips of crust. This has resulted in the isolation of basins of deposition which have both subsided and deformed independently. Five basins were formed, two of which were filled with sediments and pertain to the miogeosyncline, two with volcanics form the eugoesyncline, and a fifth composed of both volcanics and sediments forms a miogeanticlinal horst between the two. A volcano-plutonic chain was superimposed upon the fractured continental crust and the eugeosyncline was filled with material derived from the volcanoes and also from plutons of the rising batholith. The miogeosynclinal basins were filled with material derived from the continental hinterland. The eugeosyncline was deformed during the Upper Albian and the Coastal Batholith was emplaced during the Upper Cretaceous while sedimentation continued in the miogeosyncline. Deformation of the miogeosyncline occurred during the Palaeocene. Aubouin's distinction of Andean from Alpine chains is confirmed. Andean chains are characterised by andesite volcanics and tonalite batholiths, whereas Alpine chains contain ophiolite belts and sedimentary flysch. The differences may reflect their different tectonic setting, the Andes having developed under a convergent regime between a continent and a large ocean while the. Alpine chains may have evolved under a regime involving the opening and closing of small ocean basins between continents. It is suggested that andesite volcanics and tonalite batholiths are characteristic indicators of the subduction process at continental margins.

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